Standard image capture systems such as photographic images are two-dimensional representations of the three-dimensional world. The process of transforming the three-dimensional real-world into the two-dimensional images is best represented through projective geometry. In particular, much of the information which is lost in the transformation is the distance between the camera and a point in the real-world. There have been a variety of methods which have the intent of retrieving or recording this type of information. Stereo images are a common example of such a process. Others, such as a scanner from Cyberware, Inc. scan a line of laser light across a scene and from variations in the reflected light estimate the range to the object. Another method pioneered at Sandia National Laboratories (see U.S. Pat. No. 4,935,616, to Scott) uses an amplitude modulated light source and a modulated image intensifier to effect destructive wave interference patterns. A series of images are taken by phase shifting either the illumination modulation or the image intensifier modulation. After the images are captured they are processed on a pixel-by-pixel basis to ascertain the range from the camera to the object for that pixel.
The method of image capture taught by Scott and subsequent methods employing Scott's design utilize a digital image capture system, such as a CCD, array. There are several reasons why this approach has been used. The first is that each image of the series has to be registered precisely in order for subsequent range analysis to be meaningful. A second reason is that because the images are to be digitally processed, having them captured in digital format is a direct processing path. In the preferred method of estimating the range as described by Scott is for two images to be captured, one with a destructive interference caused by modulating the image intensifier, and the other with the image intensifier set at a constant voltage. However, these prior art methods are disadvantaged in that image capture is in the digital format requiring large amounts of memory. In addition, spatial resolution in the captured images is limited with current digital systems, and the pixel bit depth is less than that of traditional image capture with photographic film.